This invention relates to an antenna such as a glass antenna placed on a glass window pane of a vehicle and the like and a method for setting the antenna on a window glass, and more particularly to improvement of antenna shape.
Vehicular window panes limit drivers' sight. To ensure visibility, various legal regulations are made on vehicular antennas provided on the window panes. Accordingly, the glass antennas must be designed within predetermined limitations regulations on size, width and length.
The above limitations on the shape of the glass antennas by the regulations have serious influence on performance of glass antennas which are already disadvantageous in comparison with rod antennas in point of sensitivity.
Known conventional glass antennas, such as a vehicular antenna device disclosed in Japanese Patent Publication No. 3-74845 and a loop-shaped glass antenna disclosed in Japanese Patent Application Laid-Open No. 3-1703, are not made with consciousness of the regulations, but are well-designed in antenna shape. Further, an antenna according to an article "Disc Shaped Mono-Pole Antenna with Wide Range and Directivity-less Reception Performance" (by Michiaki Ito and Hajime Seki) is known.
The vehicular antenna device in Japanese Patent Publication No. 3-74845 is made based on the relation between the antenna and a metal pillar. That is, the length of the pillar is set to .lambda./2 (.lambda.: wavelength of received wave) or shorter, while the length of the antenna is .lambda./4 or shorter. Since this prior art is made on the relation between the antenna and the pillar, and the antenna is basically a mono-pole type antenna, it includes no reference regarding a widthwise direction. Therefore, in consideration of present vehicle size, this antenna device is applicable to the FM band at most.
The glass antenna in Japanese Patent Application Laid-Open No. 3-1703 has a 200 to 1500 mm loop shape, a conductive wire is provided to connect the antenna at a feeding point in approximately parallel to a longitudinal central line of the vehicle. This prior art is made on the point of the total length of the loop antenna, however, the relation between a longitudinal length and a transversal length of the antenna is not considered. Accordingly, to clear the regulations and attain high reception performance, trials and errors with various lengths in the lengthwise and widthwise directions must be repeated within a range of 200 to 1500 mm.
The disk mono-pole type antenna as shown in the above article has a wide range performance with a round disk shape. However, this shape obstructs a driver's sight if the antenna is applied as a vehicular glass antenna. If the size of this antenna is reduced to ensure the driver's sight, a desired performance may not be attained.